Sorry,but 3 vents aint gonna cut it. You need to fix the damage to the duct you did when you "re-did" the kitchen.No,the air coming from the vents should not be blasting out of the vents unless you have a high velocity system which is not the case here. Most times the fan speed for a/c is at a medium speed(being low,med and high,high will be for heat,some manuf. take it a step further w/ med-high speeds but those are newer units usually and not yours I'm sure).Sounds to me like there could be a few things causing this. If your furnace is in need of replacement,Why? Is there a problem with the fan/blower?Does the fan even come on?Fix the vents you disconnected and as you stated ,put up some window shades to limit the heat load entering the house. ****TACT H*** You're crazy fan speed is VERY important,if your fan is on LOW the evaporator will freeze up not having enough airflow across the coil. Go back to school !!

Well, I'm not a pro, but I do know something of passive solar. You are right to block the sunlight as this causes heat in the room. My A/C blows hard from it's vents. I currently have a heat pump and it does work with the same control unit as the heater, but it is separate.. if you understand what I mean.

I'd add more vents, you can't have too many of those!!